This invention relates to a method of fabricating semiconductor devices and more particularly to the fabricating steps to be performed after the attachment of electrodes to semiconductor pellets.
Usually, semiconductor devices such as transistors are fabricated using a metal plate called a lead frame. The lead frame for fabricating, for example, 25 transistors has 25 lead units with the same patterns repeatedly arranged in band. Each lead unit has three leads parallel disposed and a semiconductor element (pellet) is attached by means of gold foil onto the tip portion of the middle lead while the remaining leads have their end portions connected with the electrodes of the pellet by a fine wire. The end portions of the lead unit containing the bonding wires and the pellet are molded by resin and the parts of the leads protruding out of the resin mold are covered by solder layers. Then, the dams and the tie bars connecting the leads of each lead unit and the lead units with one another are cut away to produce individual transistors. The transistors thus prepared are subjected to characteristic selection in an automatic handler and then labelled with marks representing the classes of quality.
However, this process of fabrication, which is a batch process using a lead frame having 25 lead units for 25 semiconductor devices, has the following drawbacks. (1) In every step of process, a magazine for accommodating the lead frame is need for the easy handling of the lead frame. (2) The lead frame is liable to be deformed to be caught by the magazine when it is loaded on and unloaded from the magazine, so that the chances of faults in the assembler increases. (3) Since plural transfer molding machines are used to effect resin molding, the loading and unloading of the lead frame is difficult. If the loading and unloading operation is automatized, the mechanisms of the loader and the unloader become complicated and also expensive. (4) When the individual transistors are sent to a selector, they must be sent with their positions and orientations arranged in a predetermined manner. Moreover, the transistors to be sent to the selector, which are separated from one another, have a drawback that the leads are liable to be bent.
There has been proposed a method to eliminate the above drawbacks, according to which lead frame hoop (hoop material) in the form of a band, wound on a reel, is handled in assembly. This invention is directed also to such an assembling method as using hoop material.